JP2011138672A - Battery system heating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve battery characteristics and a lifetime by preventing the deterioration of discharge characteristics caused by a low temperature and the precipitation of lithium dendrite at the time of charging by heating uniformly a lithium ion battery while charging and discharging, and keeping a proper temperature. <P>SOLUTION: The battery system comprises a first nonaqueous electrolyte secondary battery 215 which has one of a first electrode out of a positive electrode and a negative electrode and a second electrode which has polarity different from the first electrode and has a first current collection part and a second current collection part, a second nonaqueous electrolyte secondary battery which has a third electrode having the same polarity as the first electrode and a fourth electrode which has a polarity different from the first electrode and has a third current collection part and a fourth current collection part, a charge and discharge circuit which connects the first battery and the second battery in series, and an AC circuit which connects the first current collection part, the second current collection part, the first capacitor, the third current collection part, the fourth current collection part and the second capacitor in order applies an AC voltage, and heats the first and second batteries. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a battery system heating method capable of improving discharge characteristics and life of a non-aqueous electrolyte lithium ion secondary battery.

  In recent years, due to demands for improving the performance of lithium-ion secondary batteries and reducing environmental burdens, the fields of use have expanded from portable electronic devices to hybrid cars, electric cars, power storage power supplies, and so on. The performance required for the secondary battery includes a high energy density, a long life, and a wide operating temperature range.

  In order to increase the capacity, it is optimal to use metallic lithium as the negative electrode material, but in general, when metallic lithium is used as the negative electrode, the internal short circuit of the battery due to dendritic lithium produced during charging, and the active material There was a problem as a side reaction of the electrolyte solution, and sufficient performance was not obtained in both safety and life. These problems have been solved by using, as the negative electrode active material, a material whose lithium occlusion / release potential is higher than the deposition potential of metallic lithium and occlude / release lithium ions.

  However, even when these materials are used, when charged / discharged at a low temperature or at a high rate, the polarization due to the internal resistance causes a problem that the capacity is significantly reduced at the time of discharge. Similar to the case of using lithium metal, dendrites precipitate, which causes the same problem.

In addition, when discharging at 20 ° C. below zero, only about 40% of the capacity can be obtained at a discharge rate of 0.8 C compared to 28.5 ° C., and the original performance cannot be exhibited. (For example, Non-Patent Document 1)
In order to solve these problems, internal methods are used to increase the specific surface area, increase the conductive agent, reduce the viscosity of the electrolyte, and control the direction of the surface of the carbon material that can insert and desorb lithium ions. Means are shown for suppressing the performance degradation at low temperatures by reducing the resistance. (For example, Patent Document 1 and Patent Document 2)
In addition, attempts have been made to avoid the problem by heating and cooling the battery from the outside by using a heater, a heat transfer plate, and the like, so that the temperature is suitable for use. (For example, Patent Documents 3 and 4)
As a means for uniformly heating the electrode plate, a means for heating from the inside by applying a direct current to the current collector to generate Joule heat has been devised. (For example, Patent Document 5)

JP 2006-309958 A International Publication No. 2006/25376 JP 2006-156024 A JP 2008-47371 A JP 2008-277196 A

Journal of Power Sources 81-82 _1999. 867-871

However, when the specific surface area is increased or the conductive material is increased, there is a problem that the energy density of the battery is also decreased because the active material density is decreased.

Further, when the viscosity of the electrolytic solution is lowered, there is a problem that the ion conductivity is lowered due to a change in dissociation or association state of lithium ions due to a decrease in dielectric constant.
When the battery is heated and cooled from the outside by a heater or the like, the thermal conductivity of the metal oxide used as a resinous separator or positive electrode active material is small, so the thermal conductivity in the stacking direction is poor, and the heating part This will cause a temperature difference inside. In addition, there is a problem that it takes time to obtain a desired temperature uniformly.

  When direct current is passed through a current collector for Joule heating to improve battery characteristics, temperature uniformity is excellent, but there is a problem that the battery cannot be used during heating. In addition, when using multiple batteries at the same time, it must be connected in parallel, and when using batteries in series, it is necessary to put a switch between each battery, making the structure and control complicated. And has a problem that it is not economical.

In order to solve the above-mentioned problem, the present invention provides a first electrode of one of a positive electrode and a negative electrode, a second electrode having a polarity different from that of the first electrode, and having a first current collecting location and a second current collecting location. A first non-aqueous electrolyte secondary battery having an electrode, a third electrode having the same polarity as the first electrode, a polarity different from that of the first electrode, and a third current collecting point and a fourth electrode A second electrode having a current collection point, a second nonaqueous electrolyte secondary battery, a charge / discharge circuit connecting the first battery and the second battery in series, the first current collection point, A second current collecting point, a first capacitor, the third current collecting point, the fourth current collecting point, and a second capacitor are sequentially connected, an AC voltage is applied, and the first and second batteries are heated. And an AC circuit.
The present invention also includes a fifth electrode having the same polarity as the first electrode, a sixth electrode having a polarity different from that of the fifth electrode, and having a fifth current collection location and a sixth current collection location, A third non-aqueous electrolyte secondary battery and a third capacitor, wherein the charging circuit further connects the third battery in series, and the AC circuit includes the fifth current collecting point, The present invention relates to a battery system for further connecting the sixth current collecting point and a third capacitor and further heating the third battery.

According to the present invention, it is possible to simultaneously perform heating, charging or discharging of the battery, and uniform heating, and it is possible to improve deterioration of battery characteristics and lifetime due to low temperature conditions.
With this configuration, it is possible to uniformly heat the batteries connected in series without affecting the state of the battery by utilizing the difference in frequency response between lithium ion diffusion and electron transfer.

Equivalent circuit diagram in the embodiment of the present invention Configuration diagram of battery 215 in the embodiment of the present invention Configuration diagram of battery 315 in the embodiment of the present invention Current path diagram of equivalent circuit in the embodiment of the present invention Temperature rise rate graph in the embodiment of the present invention Cole-Cole plot diagram in the embodiment of the present invention

Hereinafter, a battery system apparatus according to an embodiment of the present invention will be described with reference to the drawings.
(Embodiment 1)
FIG. 1 is an equivalent circuit diagram of battery system device 109 according to Embodiment 1 of the present invention. The batteries 215 and 315 described in the equivalent circuit diagram of FIG. 1 are nonaqueous electrolyte secondary batteries. The positive electrode lead 209 of the nonaqueous electrolyte secondary battery 215 is connected to the positive electrode lead 309 of the nonaqueous electrolyte secondary battery 315 via the capacitor 501. The positive electrode lead 219 of the nonaqueous electrolyte secondary battery 215 is connected to the positive electrode lead 309 of the nonaqueous electrolyte secondary battery 315 via the capacitor 501.
The positive lead resistances 220 and 230 and the negative lead resistance 240 of the nonaqueous electrolyte secondary battery 215 are desirably at least one digit smaller than the resistance in the long side direction of the current collector. This is because if the resistance of the positive electrode and negative electrode leads is larger than the lengthwise direction of the current collector, the effect of Joule heat generation at the relevant part increases, and the uniformity of heating is impaired. The same applies to the positive lead resistances 320 and 330 and the negative lead resistance 340 of the non-aqueous electrolyte secondary battery 315.
The negative electrode lead 210 of the nonaqueous electrolyte secondary battery 215 is connected to the terminal on the unconnected side of the capacitor 401. The negative electrode lead 210 of the nonaqueous electrolyte secondary battery 215 and the positive electrode lead 319 of the nonaqueous electrolyte secondary battery 315 are connected in parallel via the AC power supply 108. The negative electrode lead 310 of the nonaqueous electrolyte secondary battery 315 and the positive electrode lead 209 of the nonaqueous electrolyte secondary battery 215 are connected via a positive electrode lead resistor 230. The AC power source 108 may include a switch 110, or may include a DC power source 107 and a switch 111.
FIG. 2 is a diagram showing a specific configuration of the nonaqueous electrolyte secondary battery 215. In the subsequent drawings, the same components are denoted by the same reference numerals, and description thereof is omitted. A positive electrode composed of a positive electrode active material 206 and a positive electrode current collector 203, and a negative electrode composed of a negative electrode active material 207 and a negative electrode current collector 204 are disposed via a separator 205, and a battery outer case (hereinafter referred to as a laminate case) obtained by laminating them. The laminate case 211 is filled with a non-aqueous electrolyte (not shown) containing a lithium salt.
Positive electrode leads 209 and 213 for current collection are connected from both ends of the positive electrode current collector 203. A connection portion of the current collector 203 with the positive electrode lead 209 is referred to as a first current collection location, and a connection portion of the current collector 203 with the positive electrode lead 213 is referred to as a second current collection location. A negative electrode lead 210 for current collection is connected from one end of the negative electrode current collector 204.
The material of the positive electrode current collector 203 and the negative electrode current collector 204 to be used is preferably a material that does not cause a side reaction with the electrolytic solution or the like at the potential to be used. It is also preferable to control the electrical resistivity so that it does not deviate from a range that is at least one digit smaller than the resistance in the long side direction of the current collector.
Specifically, pure metals or alloy materials mainly composed of aluminum and copper are preferable. For example, in the case of an aluminum alloy, an alloy containing one or more elements of silicon, magnesium, copper, and zinc can be used. In the case of copper, an alloy containing one or more elements of zinc, lead, tin, and silicon can be used. By using these, the electrical resistivity and strength can be changed. In addition, although materials such as stainless steel and titanium can be used, it is more preferable that aluminum or copper is mainly used from the viewpoint of price and mass productivity.

As the positive electrode active material 206 that can be used, any material that can insert and desorb lithium ions may be used, and examples thereof include various oxides and sulfides. For example, examples of the oxide include lithium transition metal composite oxides represented by structural formulas such as Li _x MO ₂ and Li _{x + y} M _2−y O ₄ . Here, M preferably contains at least one of nickel, manganese, cobalt, and titanium, and may contain elements other than transition metals, such as aluminum and silicon. _Moreover, Li x FePO ₄ and _{Li x Fe 1-z MnPO 4} , Li x CoPO lithium phosphorus oxides may be cited having an olivine structure represented by the structural formula such as _4.

The negative electrode active material 207 that can be used may be any material that can insert and desorb lithium ions at a lower potential than the positive electrode active material. For example, a material mainly composed of carbon, an alloy material mainly composed of tin or silicon and an oxide thereof, and a metal oxide having a spinel structure typified by Li ₄ Ti ₅ O ₁₂ are particularly preferable.

FIG. 3 is a configuration diagram of the nonaqueous electrolyte secondary battery 315. The configuration is the same as that of the non-aqueous electrolyte secondary battery 215, and only the reference number is in the 300s.
FIG. 4 shows a current path when the equivalent circuit of FIG. 1 is switched on. The current path 301 is a current path when an alternating current is applied. The current path 302 is a current path when a direct current is applied. The battery is heated by applying an alternating current from the AC power source 108 between the negative electrode lead 210 of the nonaqueous electrolyte secondary battery 215 and the positive electrode lead 319 of the nonaqueous electrolyte secondary battery 315. By flowing an alternating current through the current path 301, the positive electrode lead resistor 220 of the nonaqueous electrolyte secondary battery 215 generates Joule heat by itself, and the battery can be heated uniformly.
Usually, the DC power source 107 includes a booster circuit, a withstand voltage circuit, and a noise removal circuit in order to cope with a voltage that changes with the state of charge of the battery, and is not affected by the AC current. The amplitude of the potential is determined by an execution current value obtained from a necessary heat generation rate, a current collector resistance value, a capacitor capacity, and an applied frequency. Considering that the normal use voltage of the lithium ion battery is about 2.5V to 4.3V, it is desirable from the viewpoint of circuit load that the potential amplitude is 0.3V or less. Thus, the capacitor capacity and the frequency of the alternating current are controlled so that the value of the amplitude of the voltage when the alternating current is applied is 0.3 V or less. However, since it affects the state of charge of the battery, the capacity of the capacitor is preferably 10% or less of the capacity of the battery.
The heat flow at that time is obtained from the execution value of the alternating current 108 and the resistance value of each electrode lead. The required heat generation rate depends on the density and specific heat of the material, the battery structure and arrangement, the convection state in the periphery, and the rising speed required for the intended use. On the other hand, when charging / discharging a lithium ion battery, it is necessary to move between the positive electrode and the negative electrode by diffusing lithium ions in the positive electrode and the negative electrode material or in the nonaqueous electrolyte simultaneously with the movement of electrons. In general, the rate-determining diffusion at this time is lithium ion diffusion in the electrolyte, and its frequency dependency is considered to be slower than charge transfer.
At this time, PL MOSS et al / Journal of Power Sources, that there is a large difference between the frequency that the electron movement can follow and the frequency that the lithium ion diffusion can follow.
189, 2009, P66-71.
In other words, by using an alternating current with a frequency higher than the limit frequency that lithium ion diffusion can follow, the diffusion of lithium ions in the electrolyte cannot follow the change in potential. The battery can be heated without affecting charging / discharging.
The lower limit value of the frequency that can be actually used can be estimated by the following method. The target battery is subjected to a Cole-Cole plot by the AC impedance method with the real part as the horizontal axis and the imaginary part as the vertical axis. The limit frequency that can be followed can be estimated by reading the frequency of the base point at which the 45 ° slope of the Warburg impedance measured on the low frequency side appears. If the frequency is higher than the base frequency, the influence of lithium ion diffusion is sufficiently small and there is no practical problem. More preferably, the smaller the frequency, the better in order to reduce the degree of influence of lithium ion diffusion, but it is preferably 100 MHz or less from the viewpoint of the cost of the AC power supply.

   Volume and specific gravity of aluminum foil positive electrode current collector 203, separator 205, negative electrode active material 207, copper foil negative electrode current collector 204, and aluminum laminate case 211 of the non-aqueous electrolyte secondary battery in FIG. Specific heat is shown in Table 1. Two laminate cases 211 are used. The non-aqueous electrolyte secondary battery 315 in FIG.

From Table 1, the total volume of the nonaqueous electrolyte secondary battery is 1.36 × 10 ⁻⁶ m ³ , and the total specific heat (J / K) is 4.63 J / K. Using these two nonaqueous electrolyte secondary batteries 215 and 315 and two capacitors 401 and 501 having a capacity of 0.05 F, an assembled battery having the configuration shown in FIG. 4 is produced. An alternating voltage with an amplitude of 0.3 V is applied to the assembled battery from the alternating current power source 108 at a frequency of 1300 Hz. At this time, a path through which a current flows due to an alternating potential amplitude is a current path 301 in FIG. The resistance per battery depends on the positive electrode current collector, and the value thereof is 3.3 × 10 ⁻⁸ mΩ of aluminum and 0.0022Ω depending on the positive electrode size. Since the resistance of the lead portion is one digit or more as described above, it can be substantially ignored.
At this time, the effective value of the current flowing through the path 301, that is, the effective value of the current flowing through the nonaqueous electrolyte secondary battery 215 is calculated as 32.2A. Therefore, the heat generation rate of the nonaqueous electrolyte secondary battery 215, that is, the power (P), is 2.28 W from the power (P) = resistance (R) × effective value (I _e ). The temperature rise rate graph of FIG. 5 can be derived from the work rate of 2.28 W and the total specific heat of 4.63 J / K.
From the graph of FIG. 5, it can be seen that the equivalent circuit as shown in FIG. 4 can increase the temperature at 10 ° C. in about 20 seconds. Therefore, heating, charging or discharging of the battery, and uniform heating can be performed at the same time, and it is possible to improve deterioration of battery characteristics and lifetime due to the low temperature state. The limit frequency that can be followed was estimated as follows. As a positive electrode, a mixture of Li (Ni _1/3 Mn _1/3 Ni _1/3 ) O ₂ , polyvinylidene fluoride, and acetylene black was applied to a 15 μm thick aluminum foil and cut into a 20 mm square both vertically and horizontally. Was used. As a negative electrode, a composite material composed of a carbon material and a styrene binder was applied to a copper foil having a thickness of 15 μm and cut into a square of 21 mm both vertically and horizontally. A polyethylene microporous membrane with a thickness of 16 μm as a separator was prepared by dissolving a solvent in which ethylene carbonate and propylene carbonate were mixed at a volume ratio of 1: 1 so that the concentration of LiPF6 was 1.0 M as the electrolyte. A battery was prepared using this. FIG. 6 shows the result of measuring the Cole-Cole plot by applying an AC potential of ± 10 mV to the produced battery. In the region where the frequency is 50 Hz or less, Warburg impedance with a slope of 45 degrees appears, and if the frequency exceeds 50 Hz, the influence of lithium ion diffusion is extremely small, and there is no effect on the charge and discharge of the electrode active material It can be seen that the battery can be heated without affecting.
With this configuration, the difference in frequency response between lithium ion diffusion and electron transfer can be used to uniformly heat batteries connected in series without affecting the state of the battery.
Although FIG. 1 shows a structure in which the positive electrode and the negative electrode are arranged in parallel, the structure is not limited to the above as long as the above-described constituent requirements are satisfied. For example, in the case of having a wound structure, a more remarkable difference is seen in terms of temperature uniformity than when heat is applied from the outside by a heater or the like, and it is effective to use the battery system of the present invention. is there.

In addition, when the temperature of the lithium ion battery becomes too high, the decomposition reaction of the electrolytic solution or SEI is caused, which is not preferable. In order to avoid the above problems, the battery surface temperature may be sequentially measured, and the AC current amount may be changed according to the temperature. The temperature at that time is preferably 0 ° C. or higher and 45 ° C. or lower. This is because if the temperature is less than 0 ° C., sufficient discharge capacity and life cannot be obtained, and if the temperature exceeds 45 ° C., decomposition of the electrolyte and SEI starts to occur. Further, heating by applying an alternating current may be performed only at the initial stage during charging or discharging. After that, since the temperature of the nonaqueous electrolyte secondary battery rises due to Joule heat generation due to the internal resistance of the battery itself, heating by applying an alternating current may be unnecessary after the initial stage.
Although the above has shown the case where it consists of two secondary batteries and two capacitors for the sake of simplicity, the number of batteries is not limited as long as the above requirements are satisfied. Even when there are two or more secondary batteries, the same effect as when two batteries are used can be obtained.

  The battery system heating method according to the present invention can heat a battery simultaneously with charging and discharging, and can suppress a decrease in characteristics and a life of a non-aqueous solvent secondary battery due to a low temperature, It is particularly useful for use in cold places.

203, 303 Positive electrode current collector 204, 304 Negative electrode current collector 205, 305 Separator 206, 306 Positive electrode active material 207, 307 Negative electrode active material 209, 219, 213, 309, 313, 319 Positive electrode lead 210, 310 Negative electrode lead 211, 312 Laminate case 215, 315 Nonaqueous electrolyte secondary battery 220, 230, 320, 330 Resistance of positive lead 240, 340 Resistance of negative lead 401, 501 Capacitor 107 DC power supply 108 AC power supply 301, 302 Current path 110, 111 Switch 109 Battery system device

Claims (2)

A first non-aqueous electrolyte 2 having a first electrode of one of a positive electrode and a negative electrode, and a second electrode having a polarity different from that of the first electrode and having a first current collecting location and a second current collecting location. Next battery,
A second non-electrode having a third electrode having the same polarity as the first electrode, and a fourth electrode having a polarity different from that of the first electrode and having a third current collecting location and a fourth current collecting location. A water electrolyte secondary battery;
A charge / discharge circuit for connecting the first battery and the second battery in series;
The first current collecting location, the second current collecting location, the first capacitor, the third current collecting location, the fourth current collecting location, and the second capacitor are sequentially connected, an alternating voltage is applied, and the first and An AC circuit for heating the second battery;
A battery system. A third non-electrode having a fifth electrode having the same polarity as the first electrode and a sixth electrode having a polarity different from that of the fifth electrode and having a fifth current collecting location and a sixth current collecting location. A water electrolyte secondary battery;
A third capacitor;
The charging circuit further connects the third battery in series,
The AC circuit is for further connecting the fifth current collecting point, the sixth current collecting point, and a third capacitor, and further heating the third battery.
The battery system according to claim 1.

Images